1. Field of the Invention
This invention relates to an apparatus for dry etching, which carries out anisotropic dry etching of a thin film or a substrate with radicals or a reactive gas.
2. Prior Art
With recent high density integration of ultra LSI (large scale integrated circuits) the photolithographic technique for making wirings, contact holes, trenches, etc. by photoresist masking is based on a dry etching process with a good working precision. The dry etching process is a technique of etching a photoresist-patterned thin film by an ion bombardment effect of plasma and chemical reactions and can conduct isotropic or anisotropic etching of Al, poly-Si, Si, SiN, SiO.sub.2, silicide, etc. Recently, anisotropic etching is considered to be the best technique for fine working on LSI, because the open parts of the photoresist can be vertically etched exactly thereby. However, with smaller transistor sizes of LSI devices and smaller thicknesses of gate oxide films of MOS transistors, the influence of charged particles (ions), which are utilized during dry etching, upon semiconductor devices has been severe. That is, the charged particles incoming from the substrate surface are charged up on the gate oxide to produce a high electric field on the gate oxide resulting in damage to the gate oxide. This influence has been a recent serious problem on the reliability of MOS transistors.
In order to solve this problem, an anisotropic etching technique without utilizing ions has been recently proposed. In FIG. 11, an apparatus for hot molecular beam etching, which can accomplish anisotropic etching with uncharged radicals, is shown, as disclosed by Suzuki et al in J. Appl. Phys. 64 3697 (1988). The apparatus comprises a vacuum chamber 200, a graphite tube 201 provided on the wall of vacuum chamber 200, and a stage 204. A tungsten (W) heater 202 is wound around the graphite tube 201 to heat a gas flowing through the graphite tube 201. The tip end of graphite tube 201 is connected to the vacuum chamber 200 through a quartz shielding plate 203. A desired substrate 205 on which a material to be etched is deposited is mounted on the stage 204 and then a chlorine (Cl.sub.2) gas 206 is introduced into the vacuum chamber 200 through the graphite tube 201 from one end. The chlorine gas 206 is decomposed by heating with the tungsten heater 202 and the dissociated chlorine (Cl) is injected from the other end of graphite tube 201. As a result of adiabatic expansion of gas in vacuum and intermolecular collisions, a molecular beam of uniform momentum is injected to bombard the substrate 205 provided ahead of the graphite tube 201, thereby conducting the etching. Anisotropic etching without using ions can be performed according to this principle. Similar techniques are also disclosed by Geis. M. Wet et al in J. Vac. Sci. and Technol. B4 315 (1987), etc.
Another etching technique without using ions is disclosed in J. Appl. Phys. 56 (10), 15 Nov. 1984, where SiN, Si, etc. can be etched at room temperature with ClF.sub.3, BrF.sub.3, etc. as an etching gas without using plasma. Damageless etching can be expected from the non-use of ions and a large area etching can be also facilitated.
However, the former technique is not utilized for the production of recently required semiconductors of large area, because of a very narrow etching area (about 1 cm.sup.2) which is the largest disadvantage and also because of difficult energy control of molecules is another disadvantage since energy is given to the molecules by a differential evacuation system. On the other hand, the latter technique is not suitable for the production of recent ultra LSI devices because of the disadvantage that no anisotropic etching of fine patterns can be made.